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**Pappy** · April 16, 2020, 09:23 AM

I ran a proxy race on my track one time and we stopped for lunch right before we ran the last batch of cars which were the four fastest cars in qualifying. When we got back to racing it was about 2 degrees hotter in the raceway. All the cars in the second to last batch beat the cars in the last batch. Two degrees made one hell of a difference in the traction.

**RichD** · April 16, 2020, 11:31 AM

I do testing for a major producer of aftermarket silicone and urethane tires. I have my own HO track, so the bulk of the testing has been with HO tires, but I have tested 1/32nd tires as well. When I test at my place I try to do it at 68^oF. For one thing a 10 degree change in temperature will change the diameter of the tires by a significant amount. I test tires that are available in incremental sizes and I know from experience that with HO cars there is a definite sweet spot with respect to the tire diameter. The tire diameter affects the effective gear ratio and the magnetic downforce that the car will have. I can see changes in lap times with changes in diameter as small as 0.002 inches. I don't believe that with 1/32nd scale cars the difference would be so great, but I have not tested that. With HO tires I use a dedicated stainless steel gauge to measure the diameter, with 1/32nd tires I would have to use a caliper, which is not likely to be as accurate.
If I am testing tires I always do that on a track that is perfectly clean and has been conditioned for the type of tire that I am looking at. If you normally run on silicone tires those will leave a residue on the track, if you switch to urethane tires without removing that residue the urethane tires will quickly get coated and loose much of their grip. Once again that effect may not be so pronounced with 1/32nd tires. My 1/32nd club normally runs on silicone tires, if we are hosting a proxy race for cars with urethane tires the track will be conditioned for those and silicone tires will not be run until the proxy racing is done.
Aside from the change in diameter I have not tested for changes in grip with changes in temperature. Since I have HO tires available in incremental sizes I can at least compensate for diameter, doing that with 1/32nd tires would be very difficult.
If you are running on silicone tires those will pick up dust from the track and loose grip. Providing that the track is not located tn an especially dusty area if you keep cleaning the tires they will get up all of the dust from the track surface, at least where the tires roll. If you take a break for lunch the chances are that the track will not be as clean as it was before and your lap times would tend to be at least a bit higher.
Pappy saw the cars running faster after a break when the track temperature was higher. In that case I expect that dust was not a problem. I have run in several races where changes in the track temperature did not seem to be an issue, but if the tires had not been run for a while, like after rotating out and back in, they definitely had poor grip until they got a few laps on them.
One might expect that the tires would get softer and have more grip as the temperature went up. Testing that theory would be complicated by variables that either can't easily be controlled or that you are not even aware of.

**Pappy** · April 16, 2020, 12:29 PM

Hi Rich,

The cars got slower when the temperature went up. The last batch of cars should have all been faster according to qualifying times but everyone of them got beat by the slower cars in the second to last batch of cars.

**Kevan** · April 16, 2020, 05:48 PM

Over the last 4 years I've raced Slot cars I've noticed the lap records don't go in the height of the summer or the lows of the winter but somewhere inbetween.

**arroldn** · April 16, 2020, 05:49 PM

Thanks Butch and Rich for your comments. I still have some work to do on the #26 Alfa anyway. The tires have not been glued or trued yet. The QuickSlick cars are for the QuickSlick Proxy so no gluing or truing allowed. Rich you may be right about the silicone residue. When I put some other urethane shod cars on the track they were sliding all over the place. I have tended to run urethane as that has been the spec tire for the DaVols Forums Cup Proxy for about ten years. Lately more proxies are requiring rubber so I am learning NSR tires. I have run a silicone tire in who knows when.

Thanks again guys for chiming in.

**Cgyracer** · April 16, 2020, 06:33 PM

When I had a track In the garage I found that warm to hot temps and combination of more racers created a higher humidity in the garage environment causing the track to feel "greasy" thus slower track times. I always tried to schedule hosting a proxy on a cooler day when I could better control the temperature in my garage to be most fair to the proxy car builders and get the most out of their cars.

I guess now I do not need to worry about temperatures where my new track is located. 😜

Rob

**slothead** · April 16, 2020, 07:40 PM

This topic came up in a post from last summer on the old forum and I said I'd collect some data and see if I could find a correlation between temperature and lap times on my road course.

At this time I must state the obvious caveat: Individual Results May Vary, because there are so many potential confounding factors.

I collected temperature/humidity and lap time data for 4 of my favorite cars from various series and manufacturers. Scalextric GT40, Pioneer notchback Mustang, GB Track Chevron, and FLY Porsche 917/10. All had been fitted with PG urethane tires (not glued) and had already run a lot of laps on the track. During test sessions I ran the cars in the same order (as shown above) and in the same manner - a handful of warmup laps followed by a 25 - 31 lap time trial session. Each lap time was recorded by a stopwatch program and saved to a spreadsheet along with the session's temperature and humidity as displayed by my indoor weather station. Lap time comparisons were done on a car-by-car basis so temperature, and not a car's base speed, was the independent variable.

Session temperatures were 77, 63, 56, and 44 degrees (humidity values varied from 56% to 40%). While I have enough data to do a statistical analysis I doubt anyone here would care to read that so here's my anecdotal summary.

On Shelby-Hendrix Speedway, a 57.5' routed mdf track painted with flat latex, as temperatures (and humidity) decreased lap times went up. Every car except the GT40 had its best lap time average during the 63 degrees & 56% humidity session, but overall the average lap times increased with temperature. Lap times dipped slightly from 66 to 63 degrees, then went up consistently at the lower temperatures.

Overall, warmer meant faster. Changes were slight, generally just a few percentage points between sessions.

My 2 cents worth of input suggests a sweet spot in the low 60 degree range, and then slower as it got colder. I'll add it was not fun running over 100 laps at 44 degrees before turning the heat on and I doubt anyone or any club will opt to repeat that experimental session.

**arroldn** · April 16, 2020, 11:37 PM

I can handle the 67-68 degrees my basement normally stays at. When it gets really cold Jan-Feb it might drop to 65. I either get a sweater or turn the fireplace on low. Takes about 45 mins to get it up to 70. I think in the summer it has gotten to 70 on its on but that is when its 98-100 degrees outside.

**Mitch58** · April 17, 2020, 09:10 AM

One of our club tracks here in Oregon used to be in a garage. At the time most of us were running urethane tires. We noticed that in the winter the XPGs had the best grip but in the warmer summer weather they had too much grip making the cars tippy so we would switch to the harder PGs.

Also since we raced on odd Thursday evenings most us of were working on those days and our slot car boxes sat in our vehicles all day long at what ever temperature it happened to be. that may also have impacted the difference.

**RichD** · April 17, 2020, 09:18 AM

As I hinted at earlier when you want to study the effects of temperature you will need to hold all of the other variables constant and that can be a tall order. A lot of my testing has been done with HO T-Jet type cars, in that case the performance can fall off as the laps pile up. I especially need to keep an eye on the pickup shoes, which are critical with this type of car. I always set aside a pair of reference tires so I can put those on the car at the end of a test session. I need to make sure that the car itself is still performing as it did at the start of the session.
I have seldom seen that issue with 1/32nd cars, usually those can run for hours with little or no change in performance. All of the aftermarket tires that I have used, either silicone or urethane, have had better grip once they got polished. If you glue and true your tires the tread will have a slightly rough texture. With some tires just running a hundred or so laps on the track will get you a perfectly smooth tread, other tires may need a thousand laps. Recently my club ran in a race where hand out cars and tires were used. At the start of the race our car had less grip than the others, which I attributed to a tuning issue. By the end of the race our car was about as fast as the winner, so I believe that the tires on our car improved as the race went on.
My basement can vary a bit in temperature. I have seen temperatures as low as 62^oF and as high as 84^oF. I do like to do my testing at 68^oF, if it is cold I use electric heaters. I also have a couple of air purifiers and use a dehumidifier to keep the humidity under 40%. I have no way of cooling the basement, if I must test at higher temperatures I make a note of the temperature and the tire diameters in my report.

**SpeedyNH** · April 17, 2020, 04:18 PM

silicone tires will clean the whole track off, so urethanes will have to be run a lot of laps to put the rubber back down.

**slothead** · April 17, 2020, 04:24 PM

Both of my tracks are located in the loft area of the barn. I have to heat the space from September - May to be able to use it comfortably. The warmest I can remember the loft being was in the high 80's, and the lowest was -4 (yes, 4 below zero) one time when the furnace ran out of propane for a few days in January. The coldest it's been in my yard was -30 in January 2008. It's often below zero for a week at a time here in Maine.

I now prebuy a year's supply of propane and use a frost prevention setting to keep the loft temp no lower than 44 degrees in the winter. Now that I'm retired I use the loft everyday, mostly for watching TV and computer stuff, but I also run and work on slot cars all the time. PG tires are very consistent on my road course but if I'm doing time trials for a series of cars, such as Can Am, I do all of the cars within a few days to ensure environmental factors are the same as much as I can. With 30+ cars and time trial sessions being 30 laps in length I usually can't do an entire series at the same time.

Generally speaking, small temperatures changes do not have any measurable effect on lap times. Lap times tend to be very consistent over a time trial session. Although I haven't plotted lap times over a session I think there's often a cyclical rise and fall of speeds as I get into 'the zone' for a few laps and turn in good times then slip a bit and slow down for a few laps. I don't attribute this variance to changes in the traction of the tires. As RichD said, 1/32 scale cars are not nearly as sensitive as HO cars. Except for the small yet measurable differences in lap times due to temperature I wrote about in my prior post, I attribute performance differences to the driver.

**LegOutOfBed** · April 17, 2020, 09:30 PM

We run soft rubbers not urethanes - mainly NSR, Slot.it and Sideways.
We find in winter when track temps are down to "jacket inside" the shed, - say 55 f, times are noticeably slower than when temps are up around "shirtsleeves", - say 70 - 75f
The higher temp helps the tyres warm up with laps done, - noticeably if you are dumb enough to stick your tongue on the tyre - that lowers the shore value, so they hook up more.

We don't run when it's much hotter than that, we call it summer and are sent by our wives to play outside - mainly with BBQs, pools and ****shudder**** , hiking and cycling equipment.

**HO RacePro** · April 18, 2020, 06:20 AM

Absolutely no science behind this, but...

I have always run silicone tires on my HO cars, either solid or sponge/silicone. And it has always seemed to me -- even with a freshly cleaned track -- that after a few laps the traction improved. I supposed that the tires might be warming a bit due to friction, and that had an effect.

An alternate hypothesis is that the tires clean up the track a bit further. Or they "rubber in" the track surface a tad. Or that a thin oxide layer got scuffed off.

With the sponge/silicones tire warming may make the most sense. The silicone layer is only a few thousandths thick, and the sponge is a good insulator. It would not take much mechanical work to raise the temperature of that thin layer significantly.

There's always a temptation to find equivalences between full-scale and model racing. Everyone knows tire temperature is huge in real-world racing. In model racing? Ah, well, could be...

Ed Bianchi

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